Kate Armstrong is the founder of the insurance comparison site confused.com and was the inspiration for the web firm's crazy-haired character, Cara.
The Aussie millionairess, 51, bought Cassillis Castle near Maybole in Ayrshire five years ago and set about an expensive renovation operation.
For centuries, Cassillis was home to the Kennedy clan and featured in some of the darker episodes of Scottish history. The fourth earl of Cassillis was involved in the murder of Lord Darnley, the husband of Mary Queen of Scots in the 16th century.
However, the 600-year-old building achieved fame as recently as last year, when it featured in the BBC's "Restoration Homes" show.
It has 112 rooms, associated cottages and stable blocks and exclusive salmon fishing rights.